1. Field of the Invention
The present invention relates to a method of manufacturing a liquid ejection head, and an image forming apparatus. In particular, the present invention relates to a method of manufacturing a liquid ejection head in which a plurality of liquid ejection ports (nozzles) are two-dimensionally arranged densely, and to an image forming apparatus, such as an inkjet recording apparatus, which can form an image on a recording medium by using such a liquid ejection head.
2. Description of the Related Art
An inkjet recording apparatus causes ink droplets to be deposited on a recording medium by, in response to an image signal, ejecting inks from a recording head (print head) provided with nozzles for ink ejection, while relatively moving the recording head and the recording medium, and thereby an image is formed by means of thus obtained ink dots.
A general recording head has a structure for supplying inks to pressure chambers communicated with nozzles and driving drive elements for the pressure chambers (pressure generating element each constituted from a piezoelectric element or a heating element, for example), thereby applying pressure fluctuation to the liquid inside the pressure chamber and ejecting droplets from the nozzles.
Recently, formation of high-quality images such as picture-quality images has been desired in the field of inkjet printing, and there has been carried out an attempt at realization of outputting an image with high resolution by reducing the sizes of ejected droplets and densifying the arrangement of the nozzles.
Japanese Patent Application Publication No. 7-186386 discloses an inkjet printing apparatus having a structure in which a plurality of short head modules are in the form of staggered arrangement and attached to a frame. This inkjet printing apparatus comprises a reservoir for which each of the modules can hold an ink refill section, and whereby ejection of inks performed by each module can be examined prior to assembling the modules.
Japanese Patent Application Publication No. 6-23980 discloses an inkjet recording apparatus in which an electrode substrate formed below a diaphragm is constituted from a transparent substrate and electrodes which are patterned on the transparent substrate are also constituted from transparent conducting layers. Specifically, Japanese Patent Application Publication No. 6-23980 proposes that, by using the transparent electrode substrate and electrodes, and using a light measurement technology such as a laser Doppler method, measurement of a displacement of the diaphragm is performed. According to the technology disclosed in Japanese Patent Application Publication No. 6-23980, ejection properties can be evaluated without pouring inks into the heads.
Japanese Patent Application Publication No. 2003-326723 discloses a method of examining an actuator apparatus, the method being characterized in applying predetermined voltage to a piezoelectric element under a drivable condition and executing a step of measuring the electrostatic capacity, thereby discriminating its characteristics.
Inkjet heads with high record density (high dpi), particularly line heads, are in the form of an extremely multi-element arrangement, and thus the arrangement of the elements and wirings are highly dense. In general steps of manufacturing an inkjet head, the electrical connection of the elements (piezoelectric elements or thermal elements) inside the head (connection between each element and a circuit such as a drive IC including a switch IC) is formed at a stage in the vicinity of the final step. For example, at the final stage of the step in which the duct structure body is built up, a step for connection of a FPC (flexible printed card) and connection of the IC, or the like, is performed.
In the above-mentioned step of electrical connection, if one of thousands of elements is in poor connection, all of the head may become defective. Even if the heads are not defective, if irregularities in the characteristics of the elements are significant, image degradation such as image unevenness occurs. Thus, it is necessary to precisely evaluate the characteristics of each element.
In this regard, in the general manufacturing steps, after the electrical connection step, ink is actually filled in the head, ejection of the ink is performed, and evaluation based on the electrical connection, IC, ink duct, pressure chamber and the like is carried out.
According to the technology disclosed in Japanese Patent Application Publication No. 7-186386, evaluation is performed for each module, but it is the same as the related arts in that the evaluation is conducted by filling inks and performing actual ejection.
According to the technology disclosed in Japanese Patent Application Publication No. 6-23980, the substrate and electrodes are made transparent in order to optically detect a movement (displacement) of the diaphragm; however, the transparent substrate and transparent conducting materials are not commonly used, and thus these transparent substrate and materials may be inferior to the general substrate and electrodes in terms of costs and electrical characteristics.
The technology disclosed in Japanese Patent Application Publication No. 2003-326723 is used for electrically measuring the characteristics of the elements; however, the mechanical factors of the elements (for example, the state of attachment of the piezoelectric elements) are not reflected in a result of the measurement.
Moreover, in the electrical connection step, relatively high temperature or high pressure is mostly required in general. For example, in the case of a soldering technique, the temperature is approximately 250° C. or more, and in the case of an ACF (anisotropic conductive film) technique, the temperature is approximately 150° C. or more and the pressure to be applied is approximately 1 N or more per one terminal. According to such a general manufacturing method in which the electrical connection step using relatively high temperature and high pressure is performed at the end, high temperature and high pressure are applied to the pressure chamber which is formed prior to the electrical connection step. Therefore, there is a possibility in which the dimensional accuracy of the pressure chamber, and the like, is deteriorated due to such history of the temperature and pressure.
In the case of a multi-element inkjet head, provision of a sensor in the pressure chamber in order to sense the pressure and improve reliability is proposed; however, in such a case, it is not desirable to apply high temperature to the sensor configured with a resin or the like, and to the wiring for the sensor.